Due to its geographical environment, Taiwan area has an insufficient amount of water and has difficulty in developing new water resources. In the mean time, the amount of water use in different sectors increases continuously by the year. Particularly, the expansion in the semiconductor production capacity increases the water consumption in multiples. As a result, the companies in the Science Parks in the Taiwan area face a severe pressure on water shortage and water restriction. This makes the maladjustment of water resources become a noticeable problem. Presently, the Hsin Chu Science Park demands a newly built semiconductor process to have a water recovery ratio (recycling from the discharged water to the ultra-pure water system and other secondary water use system) of more than 85%. The required water recovery ratio for an existing plant is more than 70%. The developing Tainan Science Park demands the semiconductor plants in the park to have an overall water recovery ratio of more than 85%. Therefore, the advocacy of recovery and reuse for the process water is of great urgency.
The total organic carbon (TOC) is used as one of the indexes in the recovery of waste water in a semiconductor process. The main reason for this lies in that more than 90% of the micro contamination affecting the yield of a semiconductor process and a LCD process comes from organic compounds. The organic compounds contained in the process waste water include isopropanol (IPA), N-methyl-2-pyrrolidone (NMP), etc. Only waste water with a TOC value lower than the TOC recovery threshold will be selected to be sent to an organic compound removal system or recycled without a further treatment. On the contrary, waste water with a TOC value higher than the TOC recovery threshold will be discharged. Currently, the TOC recovery threshold is about 0.5˜5 ppm. However, at this limit, the plants face a problem of a recovery ratio lower than 70%. In order to increase the recovery ratio, the industry proposes to increase the TOC recovery threshold to increase the amount of waste water entering the organic compound removal system and increase the recovery ratio to more than 70%. However, if the TOC recovery threshold is increased, the organic removal techniques (e.g. activated carbon adsorption, reverse osmosis filtration, bio-bed filtration, etc.) used by the industry will lose their functions due to the limits of the techniques which are in the range of 0.5˜5 ppm. In an activated carbon adsorption technique, the competitive adsorption/desorption reactions of the active carbon will cause the processed water having a too wide variation of the water quality. In a reverse osmosis filtration technique, the TOC removal ratio is low and bacteria are liable to grow. And in a bio-bed filtration technique, functions of the bio-bed are liable to be lost due to a large fluctuation of the water quality. Having their existing technical bottlenecks in need of being solved, the abovementioned techniques are helpless in the treatment of waste water with a higher content of organic compounds, and can not achieve the demand of increasing the process recovery ratio. This is a huge blow to an industry which faces an ever increasing water consumption due to the construction of new plants to achieve an economical production scale while facing a tight domestic water supply and difficulties in creating new water resources. Moreover, a UV/Ozone high level oxidation method has long been used to successfully removing organic compounds. It can completely oxidize organic compounds into CO2. This is different from a physical treatment method (e.g. activated carbon adsorption, reverse osmosis filtration, etc.) where the organic compounds are isolated in a certain area of the system such that the ultra-pure water system faces a potential of being re-contaminated. Moreover, the performance of a UV/Ozone high level oxidation method has been rather stable and is far higher than that of a biological treatment method. So far UV/Ozone has not been successfully and effectively applied on the removal of high concentration of organic compounds from waste water of the semiconductor and LCD processes. Thus, the present invention tries to develop such a system.
The following table discloses the comparisons between the present invention and prior arts in terms of functions, measures and results:
Description ofU.S. Pat.differences with theNo.TimeInventorDescription of patentpresent invention4,792,4071988Zeff et al.Combining ozone, UVThe present invention4,849,1141989and H2O2 in treatingadds no H2O2 and usesmethylene chloride,UV/ozone to treatmethanol andwaste water dischargedhalogen-containingfrom semiconductormaterial in undergroundand LCD processes.water, industrial wasteAnd the organicwater, and drinkingcompounds to bewater.treated are different.4,863,6081989Kawai etThe prior arts remove aThe present invention5,302,3561994al.minute amount of TOC inuses a UV/ozone5,395,5221995Shadmanwater or disclose aprocess to treat the5,868,9241999et al.treatment unit in anwaste water discharged6,030,5262000Melansonultra-pure waterby semiconductor andet al.treatment facility. TheLCD productionNachtmantreatment process mainlyprocesses that has aet al.comprises ahigher concentration ofPorterphoto-catalyzed reactionTOC than that of theand uses a coating ofprior arts in the leftTiO2, SrTiO3 or Pt, Pd,column. Moreover, theRu, RuO2 and Rh and anprocess and device usedirradiation of a UV lampare different.to decompose organiccompounds.4,990,2601991PisaniUses a cavitation deviceThe present inventionand a UV reactor to treatuses a UV/ozonewater for industrialprocess.cleaning and treat waterwith water quality of 18MΩ-cm, dissolvedinorganic solid materialof 1 ppt and TOG of100 ppb to TOC of 10 ppb.5,573,6621996Abe et al.Treats waste water with aThe present inventionlow TOCuses a UV/ozone(TOC:0.5˜3 ppm) toprocess.<1 ppb. The treatmentprocess comprises RO,vacuum stripping, lowpressure UV reactor andmixing bed.